Technologies have been developed and put to practical use which ensure safe driving of a vehicle through detecting a state of the driver of the vehicle based on, for example, the direction of driver's line of sight and biological information about the driver (e.g. eyelid behavior and heart rate) and, when the driver is found inattentive, alerting the driver. Moreover, in recent years, vehicles have been introduced which automatically perform some of the driving operations (e.g. traveling, turning, and stopping) on behalf of the drivers to reduce the driving burden on drivers. It is also expected that automatically driven vehicles which can automatically perform all of acceleration, steering, and braking while allowing human drivers to take over the driving operations in an emergency will also be introduced for practical use soon.
An object of automated driving is to reduce the driving burden on drivers. Therefore, it is conceivable that as the drivers trust automated driving more strongly, the drivers leave more driving operations to the automated driving while taking risks a little bit more. As a result, there is a concern that the drivers are going to become more relaxed and inattentive during driving. If a driver becomes inattentive during driving and becomes unable to take action in an emergency, safety cannot be ensured in the event of an emergency. Hence, in proposed technologies to reduce the driving burden on a driver and to ensure driving safety, the state of the driver is monitored during automated driving, too. When the driver is found intolerably inattentive, the driver is alerted (Patent Literatures 1 and 2). The tolerable degree of driver's inattentiveness during automated driving may be desirably not much different from a tolerable degree during manual driving from the viewpoint of ensuring safe driving. This, however, may reduce the advantages of automated driving. Hence, in proposing the technologies in the above patent literature, various studies have been made concerning a maximum tolerable degree of driver's inattentiveness during automated driving.